New Study on the Late Triassic Pollen Record at the Petrified Forest National Park, Arizona, USA

This is a new study of the palynology of the Chinle Formation of Petrified Forest National Park that fills in a previous sampling gap caused by reevaluation of the local stratigraphy. The study finds three pollen assembalge biozones that correspond to the two zones previously recovered by Litwin et al. (1991). Two main points of the paper are: 1) these faunal zones no longer pertain to the Carnian/Norian boundary as recent dating of the Chinle Formation in conjunction with a recalibration of the Late Triassic timescale demonstrates that the Chinle Formation is Norian-Rhaetian in age (Irmis et al., 2011; Ramezani et al., 2011); 2) the floral turnover roughly corresponds stratigraphically with the faunal turnover precisely located in the park by Parker and Martz (2011). Potential causal mechanisms remain under investigation.

Abstract - Recent paleontological investigations and lithostratigraphic revisions reveal a marked biotic turnover zone within the continental deposits of the Sonsela member of the Chinle Formation (Late Triassic, Norian) at Petrified Forest National Park, USA. Within the Sonsela member we found three pollen assemblage biozones: Zone II (90.5–94 m above the Mesa Redondo member) contains a relatively diverse palynological assemblage, with a mix of pteridosperms, voltzialean and some Mesozoic conifers. Following a 2.3 m hiatus, Zone IIIa (96–97.5 m) is characterized by a decrease in pteridosperms and Mesozoic conifers and a drop in voltzialean conifer diversity. The alleged voltzialean conifer pollen Klausipollenites gouldii was dominant in this part of the assemblage and a significant rise in spores and cycad pollen was also evident. In Zone IIIb (97.5–98.5 m) diversity increases and several taxa, which were absent in Zone IIIa reappear, although K. gouldii remained the most abundant taxon. The transition between the palynological assemblages Zones II and IIIa coincide approximately (within a ~2.5 m interval) with a documented faunal turnover. The floristic assemblages suggest that the climate of the south-western United States during the Norian was most likely semi-arid and highly seasonal, despite being located at tropical latitudes, with aridification occurring towards the end-Triassic as the continent drifted northwards and global volcanism increased. The gymnosperm dominated palynofloral assemblage as opposed to the fern- and horsetail-dominated macrofossil record of the Sonsela member of the Chinle Formation, conforms to a semi-arid upland environment alternated by riparian, swampy lowland.

Parker, W. G., and J. W. Martz. 2011. Constraining
the stratigraphic position of the Late Triassic (Norian) Adamanian Revueltian
faunal transition in the Chinle Formation of Petrified Forest National Park,
Arizona. Earth and Environmental Transactions of the Royal Society of Edinburgh
101:231-260.

Followers

About Me

My name is Bill Parker and I am a paleontologist in northeastern Arizona. While my day job mainly involves roaming the badlands of Petrified Forest National Park picking up bit after bit of phytosaur scrap (and finding some good stuff in-between), thus my main focus is the paleontology of the Triassic Period. However, I also have a very strong interest in Civil War history, and am a direct descendent of veterans who fought on both sides. Note: This is a personal site and all posts are my own opinions and do not represent the opinions of the National Park Service.